l-Cysteine production by metabolically engineered Corynebacterium glutamicum
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l-Cysteine is a commercially important amino acid. Here, we report the construction of l-cysteine-producing Corynebacterium glutamicum using a metabolic engineering approach. l-Serine O-acetyltransferase (SAT), encoded by cysE gene, is a key enzyme of l-cysteine biosynthesis, because of its feedback inhibition by l-cysteine. Therefore, we introduced a mutation into the C. glutamicum cysE gene, which appeared to desensitize SAT against feedback inhibition by l-cysteine. We successfully produced l-cysteine by overexpressing this mutant cysE gene in C. glutamicum, while the wild-type strain scarcely produced l-cysteine. To enhance the biosynthesis of l-serine (a substrate for SAT), a mutant serA gene, encoding D-3-phosphoglycerate dehydrogenase to desensitize it against feedback inhibition by l-serine, was additionally overexpressed in the mutant cysE-overexpressing strain and its l-cysteine production was indeed improved. Moreover, we disrupted the ldh gene encoding l-lactate dehydrogenase and the aecD gene encoding cysteine desulfhydrase to prevent the formation of lactic acid as a by-product and degradation of l-cysteine produced at the stationary phase, respectively, which resulted in enhanced l-cysteine production. However, since the concentration of l-cysteine produced still decreased at the stationary phase despite the aecD disruption, NCgl2463 encoding a possible cystine importer protein was further disrupted to prevent cystine import, because the produced l-cysteine is immediately oxidized to cystine. As a result, the time before the start of the decrease in l-cysteine concentration was successfully prolonged. Approximately 200 mg/L of l-cysteine production was achieved by overexpression of mutant cysE and serA genes and disruption of aecD and NCgl2463 genes in C. glutamicum.
Keywordsl-Cysteine Cystine import protein homologs Corynebacterium glutamicum Metabolic engineering
Authors thank Professor Iwao Ohtsu and Dr. Yusuke Kawano (University of Tsukuba) for their technical support in measurement of l-cysteine concentration by Gaitonde method, and the Biomaterials Analysis Division (Tokyo Institute of Technology) for technical assistance in DNA sequence analysis.
This work was financially supported by Science and Technology Research Promotion Program from the Ministry of Agriculture, Forestry and Fisheries of Japan. It was also supported in part by JSPS KAKENHI Grant Number JP16K14881.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
This article does not contain any studies with human participants or animals performed by any of the authors.
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